The idea of monitoring human activity, or a physical value such as a temperature, a pressure, or the like, is not new. Conventionally monitoring consists in comparing the current value of a signal representing such activity or physical value at one threshold at least, an alarm being triggered if the signal crosses a threshold.
When the alarm is triggered, action is taken either manually or automatically to bring the signal down again below the threshold.
The action being triggered subsequently to the threshold being crossed by the signal, the signal remains above the threshold between the moment the alarm is triggered and the moment when the action taken as a result of the alarm produces its effect. The period during which the signal remains above the threshold may, therefore, be important. This may have harmful consequences to security--more particularly, if the monitored signal indicates temperature or pressure.
The fact that the monitored signal remains above the threshold for a considerable period may also lead to the blocking of the monitored system--more particularly, when the monitored system takes the form of a network, such as a telecommunications network or an electric power supply network.
Such a network comprises nodes interconnected by lines which carry the telephone conversations or electric current. The flow capacity or maximum load of a line being limited, the satisfactory management of the network requires the monitoring of the particular load on each line at any moment to prevent its exceeding a predefined threshold fixed at a value lower than the maximum possible load on the line.
In known manner in the case of a telephone network, the load on a line is regulated by refusing that part of the load which exceeds the threshold. In the case of an electric power transmission network, regulation can consist in modifying the path which the power follows from one node to another. However, this may lead to other line becoming saturated, thus gradually causing a blockage throughout the network.
The general principle of the prior art monitoring methods consists in comparing the current value of the signal with a threshold, an alarm being triggered if the level of the signal is higher than the threshold.